1972 k10 brake help

[kylenautique]

So I need some advice. My brakes are not working very well, and I searched the fourms on this site, and well now I'm posting. The pedal would go almost to the floor and the brakes would hardly grab. The truck has new front calipers and new rear shoes/wheel cylinders. Original booster, proportioning valve, and Master cylinder. I removed the master cylinder and replaced with with a new one. I bench bled it and made sure all the air was purged. I installed it, and bled the truck brakes. Nothing really came out of the rear wheel cylinders, just dribbled out. Lots of fluid came out of the front. I drove the truck and the brakes felt the same. I inspected the pedal and noticed there was over 1/4 in of play so I adjusted the pedal. Now the brake pedal doesn't go to the floor. I re bled everything and more fluid came out of the rears, fronts were the same. The braking is a little better, but still not good. The pedal doesn't go to the floor and feels real hard after pushing it down, but the truck doesn't really stop. Possible bad booster? Proportioning valve? I need help!!! Any advise would be great! I'm pulling my hair out here!!!